1. Field of the Invention
The present invention relates to a liquid-crystal cell and, more particularly, to an electrode structure of electrodes arranged in a liquid-crystal cell.
In recent years, liquid-crystal display elements have been widely applied to display apparatuses. In particular, a matirx liquid-crystal display element is applied to, e.g., a television for displaying moving images. In a so-called X-Y matrix liquid-crystal element, a large number of transparent stripe electrodes are respectively aligned on two glass substrates, and these glass substrates are arranged so that their transparent stripe electrodes are perpendicular to each other. A liquid-crystal material is sealed between the two substrates. One group of transparent electrodes serves as scanning electrodes (X electrodes), and the other group of transparent electrodes serves as signal electrodes (Y electrodes). When a scanning signal is sequentially applied to the scanning electrodes at given intervals and an image signal to be displayed is applied to the signal electrodes, an image is displayed by pixels corresponding to intersections between both the electrodes.
In a method of driving the X-Y matrix liquid-crystal display element, m signal electrodes are vertically divided into two groups by a central portion C of the element, as shown in FIG. 1. Upper half scanning electrodes X.sub.1, X.sub.2, . . . , X.sub.N/2 of n scanning electrodes are combined with upper half signal electrodes Y.sub.1A, Y.sub.2A, . . . , Y.sub.mA, and remaining (lower) half scanning electrodes X.sub.N2, X.sub.(N/2+1), . . . , X.sub.N are combined with lower half signal electrodes Y.sub.1B, Y.sub.2B, . . . , Y.sub.mB. The two combinations of the electrodes can be driven as if they were independent X-Y matrix liquid-crystal display elements. This method has been disclosed in Japanese Patent Disclosure No. 59-186985 and in U.S. Pat. No. 4,541,690. With this drive method, a high contrast ratio and a high response speed can be expected.
FIG. 2 shows an enlarged electrode structure of the X-Y matrix liquid-crystal cell driven by the above method. Scanning electrodes 1 are aligned on a glass substrate 10 in the form of strips to be vertically separated from each other by a distance d, and signal electrodes 2 are aligned on a glass substrate 20 in the form of strips to be horizontally separated from each other by a distance e and to be separated by a distance l from the opposing signal electrodes at a central portion C in the longitudinal direction thereof. Since the intersection between the scanning and signal electrodes 1 and 2 (indicated by coarse hatching) serves as a pixel G, the distance l is selected to be smaller than the distance d so as not to influence a displayed image.
In terms of mass-production, the distances d, e, and l for the electrodes 1 and 2 fall within the range of at most 10 to 20 .mu.m due to limitations in the manufacture thereof (e.g., a print technique), and it is impossible to make the distance l smaller than the distance d by any great degree. As a result, in the manufacture of the liquid-crystal cell, when the glass substrate 20 on which the signal electrodes are formed and the glass substrate 10 on which the scanning electrodes are formed are adhered by a sealing agent, if the relative positions of both the substrates are shifted, an area S.sub.1 of a pixel G.sub.1 becomes smaller than an area S.sub.2 of a pixel G.sub.2 by a solid area Q under the influence of the central portion C of the signal electrodes 2, as shown in FIG. 3. For this reason, when the liquid-crystal cell is driven by applying a voltage to the electrodes 1 and 2, a non-illuminated portion of the central portion becomes wider than that of other portions, and a white line is undesirably displayed on the central portion of a screen, resulting in poor display. More specifically, referring to FIG. 2, if the distance l is set to be 10 .mu.m and the distance d is set to be 20 .mu.m, distal ends A (indicated by fine hatching) of the signal electrodes 2 at the central portion C are respectively 5 .mu.m. When the shifting between the glass substrates exceeds 5 .mu.m, the area S.sub.1 of the pixel G.sub.1 begins to decrease, and a white line appears along the central portion C of the signal electrodes 2 (i.e., at the central portion of the screen). Therefore, a tolerance for shifting between the two glass substrates is .+-.5 .mu.m. FIG. 3 shows a case wherein the glass substrate 20 with the signal electrodes 2 shifts downward with respect to the glass substrate 10 mounting the scanning electrodes 1. Conversely, if they shift upward, the same phenomenon as above occurs.
In the steps in the manufacture of the conventional liquid-crystal cells, in order to keep a relative positional precision between the two glass substrates, assembly is performed while the shifting of the relative positions is corrected several times before the sealing agent for adhering the substrates is hardened. For this reason, this undesirably increases the number of assembly steps and, in spite of this, it is still difficult to yield a perfect product. In addition, the manufacturing cost is thereby increased, resulting in expensive products. In the manufacture of the liquid-crystal cells, transparent electrode patterns for a plurality of liquid-crystal cells are printed respectively on two glass substrates at the same time, and after the two glass substrates are aligned and adhered to each other through a sealing agent attached around the respective electrode patterns, the resultant structure is cut into individual cells. In this case, display quality is often degraded by shifting of photomasks for forming electrode patterns, shifting of patterning (e.g., printing or exposure), and shifting of the two glass substrates when they are adhered to each other. Therefore, it is difficult to decrease product cost.